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03-04-2021, 18:40
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#16
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,604
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Re: Stolen ballast, how important is it really?
Quote:
Originally Posted by Jim Cate
Adding 200 lbs at the top of the existing 3000 lb ballast will not, IMO, have a "great effect" on the righting moment... one that the PO will be able to discern in his use of the boat.
Jim
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Jim
I think I should have said 400lb but anyway I think we would have to have a computerized brain to work out all the variables of boat stability and come up with an ideal boat.
I don't want to breach copyright so can only cut-n-paste a very small section of an excellent article (but the whole article is really well worth reading)
" It is helpful to perform a few basic calculations... For example, assume we have 2,000 pounds of ballast located 5 feet from the roll axis. This will provide a Righting Moment (Torque) of 5 * 2,000 = 10,000 lb-ft however it will yield a Roll Moment of Inertia of 5^4 * 2,000 = 1,250,000 lb-ft^ Much more dramatic is to consider a 200 pound mast having its CG located 25 feet above the roll axis. The mast will introduce a Heeling Moment of 25 * 200 = 5,000 lb-ft, but will have a Roll Moment of Inertia of 25^4 * 200 = 78,125,000 lb-ft^4.
In this example, the mast exerts exactly half the static moment (torque) as compared to the ballast, but although the mast has only one tenth the mass of the ballast, by virtue of its distance from the roll axis the mast is some 62.5 times more effective at resisting being put into motion...!! It is by this simple example that we can observe the extraordinary benefits conferred by well-distributed masses
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Many years ago during the Fastnet Race, rigorous analyses done after the loss of many vessels revealed that the boats which had concentrated ballast, light structure, and very light rigging suffered excessively due to their harsh rolling motions which caused many dismastings with consequent capsizes, as well as widespread seasickness and inability to function.
By comparison, boats with heavier structure, lesser "ballast rati......."
http://www.kastenmarine.com/beam_vs_ballast.htm
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04-04-2021, 17:42
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#17
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Registered User
Join Date: Sep 2012
Location: Tasmania
Boat: Cutter rigged Tahitiana
Posts: 45
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Re: Stolen ballast, how important is it really?
For anyone interested; have a read of 'Seaworthiness, the Forgotten Factor' by CA Marchaj - brilliant and accessible exposition of the interplay of all factors influencing stability and sailability.
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04-04-2021, 17:50
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#18
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Registered User
Join Date: Mar 2013
Location: Santa Cruz
Boat: 1975 Isander 28
Posts: 132
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Re: Stolen ballast, how important is it really?
I actually have lead and not afraid to smelt it, plus I am already a retarded juvenile, so no problem there. But there are issues like how to design the molds, how to fasten the blocks, also how to inspect and clean the keel-bolts underneath regularly, etc. makes me reluctant to actually do this unless someone gives me really good reason to. The crack about jail time was tounge and cheek, I just don't want to do it unless it really will help measurably.
Could this ballast help with either the weather helm into the wind or broaching when running? These are the two areas that could use some improvement.
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04-04-2021, 19:00
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#19
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Moderator
Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 14,305
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Re: Stolen ballast, how important is it really?
As an owner of a tender boat, I have considered adding ballast. In fact the builders of my boat did add a thousand pounds more of lead after a couple years of production. But the designer wasn't dumb, he knew what he was doing in calculations. Now it may be that adding that weight does give it some measure of stiffness that may benefit it going upwind. YOur bilge is kinda shallow though so it wasn't much below the waterline. Still, any weight below the waterline is a good thing. Your former owner may have been trying for a small racing advantage, but your boat should sail fine as is. If you need to balance out the engine you might try buying 200' of 1/4 chain and stow it under the v-berth.
My rigger friend keeps bugging me to get more ballast and his argument is that any weight below the waterline helps to lower the whole boat which lowers the center of gravity and improves stiffness.
__________________
DL
Pythagoras
1962 Columbia 29 MKI #37
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04-04-2021, 19:46
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#20
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,604
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Re: Stolen ballast, how important is it really?
Quote:
Originally Posted by skkeith
I actually have lead and not afraid to smelt it, plus I am already a retarded juvenile, so no problem there. But there are issues like how to design the molds, how to fasten the blocks, also how to inspect and clean the keel-bolts underneath regularly, etc. makes me reluctant to actually do this unless someone gives me really good reason to. The crack about jail time was tounge and cheek, I just don't want to do it unless it really will help measurably.
Could this ballast help with either the weather helm into the wind or broaching when running? These are the two areas that could use some improvement.
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My mold was just a steel "U" beam and I used sheet-metal "dividers" hammered in at the appropriate length. By raising one end I was able to make tapered "ingots" which I used appropriately to follow the shape of the keel. Some of the ingots in the background I bought
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05-04-2021, 03:18
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#21
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Marine Service Provider
Join Date: Dec 2010
Location: Little Compton, RI
Boat: Cape George 31
Posts: 2,978
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Re: Stolen ballast, how important is it really?
Quote:
Originally Posted by coopec43
Jim
I think I should have said 400lb but anyway I think we would have to have a computerized brain to work out all the variables of boat stability and come up with an ideal boat.
I don't want to breach copyright so can only cut-n-paste a very small section of an excellent article (but the whole article is really well worth reading)
" It is helpful to perform a few basic calculations... For example, assume we have 2,000 pounds of ballast located 5 feet from the roll axis. This will provide a Righting Moment (Torque) of 5 * 2,000 = 10,000 lb-ft however it will yield a Roll Moment of Inertia of 5^4 * 2,000 = 1,250,000 lb-ft^ Much more dramatic is to consider a 200 pound mast having its CG located 25 feet above the roll axis. The mast will introduce a Heeling Moment of 25 * 200 = 5,000 lb-ft, but will have a Roll Moment of Inertia of 25^4 * 200 = 78,125,000 lb-ft^4.
In this example, the mast exerts exactly half the static moment (torque) as compared to the ballast, but although the mast has only one tenth the mass of the ballast, by virtue of its distance from the roll axis the mast is some 62.5 times more effective at resisting being put into motion...!! It is by this simple example that we can observe the extraordinary benefits conferred by well-distributed masses
.
Many years ago during the Fastnet Race, rigorous analyses done after the loss of many vessels revealed that the boats which had concentrated ballast, light structure, and very light rigging suffered excessively due to their harsh rolling motions which caused many dismastings with consequent capsizes, as well as widespread seasickness and inability to function.
By comparison, boats with heavier structure, lesser "ballast rati......."
http://www.kastenmarine.com/beam_vs_ballast.htm
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IIRC, Skene advocates bolting some of your ballast to the underside of the side decks to bring the weight UP and make the roll period better. Seems counterintuitive to me, but Skene was very well regarded even after his day had passed.
__________________
Ben
zartmancruising.com
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05-04-2021, 03:20
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#22
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Marine Service Provider
Join Date: Dec 2010
Location: Little Compton, RI
Boat: Cape George 31
Posts: 2,978
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Re: Stolen ballast, how important is it really?
Quote:
Originally Posted by coopec43
My mold was just a steel "U" beam and I used sheet-metal "dividers" hammered in at the appropriate length. By raising one end I was able to make tapered "ingots" which I used appropriately to follow the shape of the keel. Some of the ingots in the background I bought
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Cooper, this is genius! I made all my ingots in bread pans, which left a lot of little gaps to fill.
__________________
Ben
zartmancruising.com
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05-04-2021, 04:34
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#23
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,604
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Re: Stolen ballast, how important is it really?
Quote:
Originally Posted by Benz
Cooper, this is genius! I made all my ingots in bread pans, which left a lot of little gaps to fill.
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Glad you like the idea!
It worked out very well as I could select the thickness and taper of each ingot. (The lead as laid would be very close to a solid block) The front compartments have 4 layers, mid about 3 layers and aft about two layers.
I had to do some cutting with my circular saw. I had a tarp under the saw to catch the "saw dust" which of course I poured into any little gaps.
Then I poured polyester resin to fill any gaps so the ingots couldn't move (and make the keel like a solid block. I then heavily fiber glassed over the top of the ballast.
But the trim ballast is loose and just laying there. Once the yacht is in the water I'll move the trim ballast to its permanent place and fiberglass over it just as I have done to the rest of the ballast.
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05-04-2021, 05:15
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#24
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,604
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Re: Stolen ballast, how important is it really?
I should have mentioned all the "ingots" are laid fore and aft on their edge so that I could select tapered ones where the keel was narrowing. I did have photos of the laid ingots but then the camera carked it.
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09-04-2021, 06:57
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#25
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Registered User
Join Date: Feb 2010
Location: New Orleans, LA
Boat: Figment 40
Posts: 9
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Re: Stolen ballast, how important is it really?
Islander 28 is a Bob Perry design. One of his best, so. Congratulations on getting a nice boat. I suggest you reach out to the "Maestro" on the FB page "Friends of Bob Perry, Yacht Designer, Fan Club" page. I'm sure he can tell you a lot about the ballast.
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09-04-2021, 07:29
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#26
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Registered User
Join Date: Aug 2010
Location: Naples, FL
Boat: Leopard Catamaran
Posts: 2,572
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Re: Stolen ballast, how important is it really?
Quote:
Originally Posted by Jim Cate
Adding 200 lbs at the top of the existing 3000 lb ballast will not, IMO, have a "great effect" on the righting moment... one that the PO will be able to discern in his use of the boat.
Jim
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Depends on hull curvature.
Boats have capsized from deviating too far from designed waterline.
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09-04-2021, 07:47
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#27
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Registered User
Join Date: Feb 2013
Location: WY / Currently in Hayes VA on the Chesapeake
Boat: Ocean Alexander, Ocean 44
Posts: 1,149
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Re: Stolen ballast, how important is it really?
Quote:
Originally Posted by eddiestubbs
Islander 28 is a Bob Perry design. One of his best, so. Congratulations on getting a nice boat. I suggest you reach out to the "Maestro" on the FB page "Friends of Bob Perry, Yacht Designer, Fan Club" page. I'm sure he can tell you a lot about the ballast.
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This.... It would be well worth a consultation fee to get it right!
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09-04-2021, 09:09
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#28
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Registered User
Join Date: Jul 2013
Posts: 6
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Re: Stolen ballast, how important is it really?
Hi Skkeith,
I too have an I28 with funky keel bolts. Could you share how you plan to sister the keel bolts? My understanding is that the lag bolt method is not very secure due to the malleability and creep of the lead against the threads. I was contemplating drilling down for a threaded rod and then sideways into the keel to form a nut pocket.
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09-04-2021, 13:44
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#29
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Registered User
Join Date: Feb 2013
Location: traveling
Boat: Islander 32
Posts: 27
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Re: Stolen ballast, how important is it really?
Maybe a little off topic but as was mentioned that the balast up so high wouldnt help your righting moment. Maybe look into adding a fin on the bottom of your keel. If you want that effect maybe a good idea but if you are just a weekend user continue with your plan.
Im curious, though, i have a 1979 islander 32 and couldnt be happier. I consistently get 4 - 6 knt. With the genoa alone in fairly light air. Why is your islander a mistake???
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09-04-2021, 15:20
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#30
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Registered User
Join Date: Mar 2020
Location: Hamble
Posts: 33
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Re: Stolen ballast, how important is it really?
Are there no engineers on here?
Adding ballast in the centre of the boat changes the polar moment of the boat, thus changing pitching period.
Ballast added internally doesn't greatly affect heel at low angles, but as heel increases, the distance from ballast to heeled centre of buoyancy increases until(sometimes) past 90degrees.Many trailer sailers have small light centreboards/keels, and rely on internal ballast to stop capsizing.
A lost mast will not capsize the boat. If anything,a sailboat with mast removed would end up nearly unable to be capsized.
All just common sense.
There was a mention about the 79 Fastnet. I was there, on an Admiral's Cup team boat. No raceboats were lost, but a few were forced to be abandoned then picked up by local trawlers. The couple of boats that were lost were cruisers of poor design, and took on water when excessively heeled but not as far as 90degrees.
In IOR raceboat days, lead ballast, sometimes in large amounts, was used to trim the boats to affect immersion depths, thus affecting rating(or handicap) Bow down trim was encouraged by the rule, but made the boats pigs to sail.
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